Longest common subsequence string LCS

[EDIT: 20110603 09:53 CDT - reformat - WDR]

can some one help correct this matlab code for the recursive Longest common subsequence string LCS, the error "Subscripted assignment dimension" when run the following code

the function rec read two string from files the call the temp to fill the LCS table recursivly

function rec()
%to read the two strings from files
%x1='xyxxzxyzxy';
%x2='zxzyyzxxyxxz';

fid1=fopen('file1.txt');
fid2=fopen('file2.txt');

chs1 = textscan(fid1, '%c');
chs2 = textscan(fid2, '%c');

fclose(fid1);
fclose(fid2);

global x1;
global x2;
x1 =char(chs1);
x2 =char(chs2);
%to read the two strings from files

%creat a global table then call temp func to fill in
lenx1= length(x1)+1;
lenx2= length(x2)+1;

global L;

L = zeros(lenx1,lenx2);
temp (lenx1,lenx2);

%disp (L);
end

function result = temp (m,n)

global x1;
global x2;
global L;
result = L;

if m==1 || n==1
    result(m,n) = 0;

elseif x1(m-1) == x2(n-1)
    disp(['if=' x1(m-1)]);
    disp(['if=' x2(n-1)]);
    result(m,n) = temp(m-1,n-1) + 1;

else
    disp(['else=' x1(m-1)]);
    disp(['else=' x2(n-1)]);
    result= max(temp(m,n-1), temp(m-1,n));

end
%L(m,n) = result(m,n);

return
end

[Walter Roberson]

We do not have your input files, so you will need to tell us which line the problem occurs on, and you will need to show us the size() of the left-hand side of the assignment and the size() of the right-hand side of the assignment.

[Alaa]

you can add any two strings...the error occure when the function temp return from the base state "if m==1||n==1" to start filling the table L

[Alaa]

I will be thanful if you try to help me ....

this link descibe the problem i need to code it

http://en.wikipedia.org/wiki/Longest_common_subsequence_problem#LCS_function_defined

Answer 1

[John D'Errico]

Well, you could always just use my commonsubstring function to do the work.

Of course, since this is almost surely homework, that is not really a viable option. commonsubstring is pretty fast though.